Find regions bounded by curves.

Input parameters:

1. Cr → Boundary curves.
2. Pt → Optional region seed points. If omitted, all regions will be found.
3. Cb → True to combine contiguous regions.
   •  True → Combine
   • False → Separate

Output parameters:

1. Rg → Regions based on curve boundaries and seed points.
2. Mc → List of curve indices contributing to each region.
3. Mp → List of point indices contributing to each region.